Around the World, Warmer Temperatures Mean More Infections

April 25, 2006

By JOY VICTORY

At first glance, an outbreak of diarrhea among passengers on board a cruise ship in Alaskan waters in the summer of 2004 seemed to be relatively harmless.

Health officials theorized it might be the Norwalk virus, a bug that often affects people living in close quarters, such as in nursing homes, hospitals and cruise ships. While certainly annoying, Norwalk usually doesn't cause serious illness.

But then the lab reports started trickling in, and it showed that indeed a more serious problem was at hand -- many of the afflicted the passengers had eaten raw oysters raised in Alaska that were infected with a type of cholera-like bacteria, Vibrio parahaemolyticus, that normally grows on shellfish harvested in much warmer waters.

The finding not only signaled a dangerous new risk to the Alaskan seafood industry, it also highlighted how surprisingly and directly global warming can affect human health, particularly in terms of infectious diseases, experts say.

"Depending on the warming trend that unfolds in the years ahead, we have to accept that habitats will change ... new bugs can be expected to settle in. Every organism will find a niche," said epidemiology professor Colin Soskolne, of the University of Alberta in Canada. "With the tampering of the environment, we really can't predict with much certainty exactly what those changes will be."

Not Safe for Consumption

Global warming is caused by an increase in carbon dioxide and other industrial and auto emissions, which trap heat in the atmosphere and increase air and water temperatures.

While he has personally noticed Alaska's shrinking glaciers and ice floes, global warming wasn't on the mind of Dr. Joseph McLaughlin as he investigated the cruise ship disease outbreak.

He simply wanted to know why the oysters were suddenly at risk -- before this outbreak, no seafood in Alaska had ever tested positive for Vibrio because the ocean water was simply too cold for the bacteria to multiply.

But that was no longer true: An analysis showed that Alaskan water was no longer as chilly as it once was, giving Vibrio a new home up north.

"There's a sort of threshold level, above which concentrations of Vibrio in oysters become (accumulated) enough to cause illness in humans," said McLaughlin, a medical epidemiologist with the Alaska Department of Health and Social Services in Anchorage. "That temperature is about 15 degrees Celsius. What we found was that 2004 was the first summer on record during which the temperature exceeded that."

Or as McLaughlin said in a report published in the New England Journal of Medicine last October: "Rising temperatures of ocean waters seem to have contributed to one of the largest known outbreaks of V. parahaemolyticus in the United States."

The warmer water is unlikely to go away. Buoys placed by the National Oceanic and Atmospheric Association in 1976 have detected a steady annual increase of .4 degrees in the Gulf of Alaska, he said.

"We're not talking about a little bay in Prince William Sound," McLaughlin said.

Thankfully, the state health department got the word out about the outbreak and advised oyster farm owners to keep oysters deep enough where they would not be exposed to water any warmer than about 15 degrees C.

It is just one of the many ways that Alaskans have had to adapt to documented changes in the climate and environment, McLaughlin said. But it serves as a strong warning signal.